Why is the freezer door hard to open?
After you close the freezer door, the air inside the cabinet cools down. Like most things, air contracts as it gets cooler. Because it is in a confined space, the contracting air causes the air pressure inside the freezer compartment to drop. The overall result is much lower air pressure inside the freezer than outside, so the freezer door is being “sucked” on.
The lower the temperature, the lower the air pressure and the harder it is to open the door. The freezer is colder than the fridge, so the freezer door is “sucked” on more firmly and is, therefore, harder to open.